Digital communications are making more and more use of channel coding varying from simple coding schemes to very complex ones. The principle of channel coding is to add controlled redundancy to information symbols to enable the receiver to detect the presence of transmission errors, and where applicable correct them. Existing codes include more particularly slice codes based on the principle illustrated by FIG. 1. A turbo encoder 1 uses p slices to effect coding with an efficiency of R =K/N. This turbo encoder includes an interleaver 3 and two identical encoders 21 and 22 typically effecting circular recursive systematic convolutional (CRSC) coding. The CRSC coder consists of p slices and, for each of them, encodes with an efficiency r =k/n (k is the number of input symbols and n is the number of output symbols; n−k are the redundancies produced by the encoder). Turbo encoding therefore causes an input frame of K =k×p information symbols that can be split into sub-frames Systi, Syst2, Systp each of k symbols to correspond to a frame that may be considered as p concatenated sub-frames of identical size equal to k +2×(n−k). Each sub-frame includes k information symbols and 2×(n−k) redundant symbols coming from the two encoders. The encoder 21 successively codes by blocks of k symbols the k×p information symbols from the frame present at the input. The encoder 22 successively codes by blocks of k symbols the k×p information symbols from the frame present at the input that has been entirely interleaved. For turbo coding with p slices, a turbo encoder effects 2×p successive coding operations, each taking into account k information symbols. The efficiency of the turbo encoder 1 is therefore given by the equation R =k/(2×n−k) because N =(k +2×(n−k)×p and K =k×p. For coding with p =2slices and where Y11 and Y12 denote the redundant symbols at the output of the first encoder 21 and Y21 and Y22 denote the redundant symbols at the output of the second encoder 22, the output frame consists of a first sub-frame comprising Systi, Y11 and Y21 and a second sub-frame comprising Syst2, Y12 and Y22. In a first step the first encoder 21 encodes the k information symbols Systi. In a second step it encodes the next k information symbols Syst2. In parallel with this, the complete frame of size 2×k consisting of Systi and Syst2 is interleaved 3 and the result of this interleaving feeds the second encoder 22. In a first step the second encoder encodes the first k information symbols. In a second step it encodes the next k information symbols resulting from the interleaving. Slice coding is described in the paper by D. Gnaedig, E. Boutillon, M. Jezequel, and V. Gaudet “On Multiple Slice Turbo Codes”, 3rd International Symposium On Turbo Codes & Related Topics, Brest, France, 1-5 September, 2003, p. 343-346.
The invention relates to decoding techniques. Decoding appropriate to slice coding uses a turbo decoder structure. This is known in the art. One such decoder is described in the paper by M. Arzel, C. Lahuec, M. Jezequel, and F. Seguin “Analog Decoding of Duo-Binary Codes”, International Symposium on Information Theory and its Applications, ISITA2004, Parma, Italy, Oct. 10-13, 2004. The decoder 4 shown in FIG. 2 appropriate to coding with two slices includes four independent individual decoders 511, 512, 521, 522, two per slice. Each individual decoder operates on a portion of the received frame. The individual decoders 511 and 521 operate respectively on the first half of the received frame and on the first half of the received frame that has been fully interleaved, and the individual decoders 512 and 522 operate respectively on the second half of the received frame and on the second half of the received frame that has been fully interleaved. In the more general case of coding with p slices, the appropriate decoder requires the use of 2×p individual decoders. With an analog decoder, this has the drawback of requiring a large area of silicon proportional to the number of slices.